This paper presents two ways of using holographic interferometry, firstly for identification of materials such as metals as regards fatigue and failure behaviour and secondly for complete determination of the state of stress in transparent plane models. 1 - After outlining the principal parameters of the linear elastic theory of failure, we demonstrate the use of real time holographic interferometry in the quantitative determination of yield phenomena at fatigue crack tips. 2 - Under certain conditions elastic behaviour study of complex structures can be confined to analysis on two dimensional models. When the state of stress changes, each point in the model simultaneously undergoes a variation of index and thickness. The first factor can be linked to the difference in stresses whereas the second is a function of the sum of stresses. The optical effect from a double exposure holographic recording will not show a simple superposition of interference fringes of different origin but rather a complex intermodulation of different curves. On the other hand, using a specific set-up and a non-reciprocal rotatory power with a FARADAY cell, it is possible to obtain simultaneously and separately the interference fringes representing the sum and the difference of stresses.